It has become evident that nitrogen and phosphorus affect the productivity of aquatic life--nitrogen being the limiting nutrient in eutrophic waters and phosphorus in oligotrophic waters.
It is also known that domestic waste waters contain from 10 to 100 times the nutrient concentration of agricultural or forest drainage. Consequently in densely populated areas overfertilization of surface waters, algae growth and chemical pollution have been noticed along with degradation of potable water sources and the need for more efficient removal of all pollutants from waste waters has become more obvious.
While removal of phosphorus can be achieved reliably by chemical precipitation and removal of organics by biological followed by physical-chemical processes, removal of nitrogen is more complicated.
The biological transformations of nitrogenous compounds occur through biological processes of ammonification, nitrification and denitrification. The first two require presence of oxygen, the denitrification require absence of oxygen. The two distinct mechanisms responsible for removal of nitrogen and reduction of nitrite and nitrate are (a)--formation of ammonia followed by transfer of ammonia into the anabolic cell metabolism which is of minor importance since C:N ratio in cell tissue is 5-6, whereas in domestic waste waters only 2 to 2.5 (b)--microbial denitrification, which is a respiratory reduction in which nitrite and nitrate replace oxygen as the final electron acceptors in the respiration chain.
Biooxidation of organic matter, ammonification and nitrification cause no problem. Nitrification is efficient and reliable if organic loadings are maintained below 0.3 lb BOD per lb of mixed liquor suspended solids per day, sludge age is maintained above 3-4 days and disolved oxygen in the mixed liquor is maintained above 1.0-2.0 mg/lit. The higher is the concentration of mixed liquor suspended solids, the more efficient is the transformation of ammonia to nitrite and nitrate. The overall rate of denitrification is a function of the concentration of the heterotrophic facultative bacteria present in mixed liquor suspended solids and their activity in the absence of oxygen. To maintain the activity the denitrifying bacteria must be supplied with suitable organic material--source of energy.
From the process point of view to accomodate the different food and oxygen requirements of biooxidation of organic matter, ammonification and nitrification of nitrogenous compounds and decomposition of nitrite and nitrate by microbial respiration and to achieve acceptable reaction rates and efficiencies, the various biochemical reactions are currently being carried out in separate process stages. While the conventional activated sludge process is capable of removing nitrogen with efficiency of 50-60 percent, the current multistage processes can achieve the removal of nitrogen with efficiency of up to 80-90 percent.
The multistage processes currently in use in large municipal treatment plants require treatment facilities that are too complex to be scaled down to small package plants to serve small developments or single family dwellings. Because of the number of process steps required for removal of the various pollutants renovation and reuse of domestic waste waters at present seems feasible only if practiced on a large scale.
A large waste water treatment-renovation plant however requires large underground sewage collection-transportation network, and in case the renovated water is to be reused also a large underground water distribution network. Such networks are expensive to build and even more expensive to maintain and to operate.
It is therefore obvious that on-site renovation and reuse of waste water would be economically more attractive than renovation and reuse of waste waters via central collection-treatment-distribution. However because of the complexity of the involved treatment on-site renovation and reuse of domestic waste waters as yet can't be practiced.
Although at present small package sewage treatment plants are available, they do not provide the required degree of purification that would permit reuse of the purified effluent and in general they also lack the required mechanical reliability.
It is therefore the prime object of this invention to provide an apparatus in which the various processes to remove all pollutants present in sanitary waters could be carried out reliably, unattended and at acceptable cost when serving single or multiple family dwellings.
More particularly it is the object of this invention to provide an apparatus that would reliably maintain all conditions required for efficient biooxidation of organic matter, biological nitrification, biological denitrification, chemical precipitation of soluble phosphates, chemical oxidation of the residual and refractory organics and toxic compounds, efficient kill of bacteria and viruses and efficient removal of the residual chemical oxidizing agents so as to render the effluent non-toxic to aquatic life and suitable for reuse.
Another object of this invention is to provide an inexpensive and reliable apparatus for storing and proportioning of the various chemicals to the unsteady or batchwise flow of the incoming waste water.
Another object of this invention is to provide an apparatus in which efficient separation of suspended solids from the effluent is achieved inside the reactor so that a separate clarifier and the associated sludge return pumping is not required.
Another object of this invention is to provide an apparatus capable of reliable and unattended operation when processing waste waters on ships under condition of ship motion and vibration.
Another object of the invention is to provide an improved suspended solids separator that would not be affected by "sloshing" that normally occurs on ships during heavy roll and pitch conditions.
Another object of this invention is to provide an apparatus that would require only once per year replenishment of the used chemicals and only once per year withdrawal of the excess sludge when serving single family or multiple family dwellings.
It is also an object of this invention to provide an apparatus capable of reliable and unattented operation when operating with wood particles such as saw dust, powdered minerals, powdered activated carbon, powdered charcoal or their mixtures in reaction chambers.
Another object of the invention is to provide an apparatus that would be easy to scale up or down to use as standardised waste water renovation system to serve small communities, camps, airports, commercial developments, recreation centers, parks and industrial plants either as a permanent or temporary installations.
Other objects and features of the invention will be seth forth fully hereinafter.
The full nature of the invention will be understood from the accompanying drawing and the following description of claims.